Implement method for finding coarsest ZonedTimeGrain

CHANGELOG.md

@@ -8,9 +8,13 @@ pull request if there was one.
 Current
 -------
 ### Added:
+- [Method for finding coarsest ZonedTimeGrain](https://github.com/yahoo/fili/pull/230)
+    * Added utility method for returning coarsest `ZonedTimeGrain` from a collection of `ZonedTimeGrain`s. This is
+    useful to construct composite tables that requires the coarsest `ZonedTimeGrain` among a set of tables.
+
 - [Should also setConnectTimeout when using setReadTimeout](https://github.com/yahoo/fili/pull/231)
     * Setting connectTimeout on DefaultAsyncHttpClientConfig when building AsyncDruidWebServiceImpl
-        
+
 - [CompositePhysicalTable Core Components Refactor](https://github.com/yahoo/fili/pull/179)
     * Added `ConcretePhysicalTable` and `ConcreteAvailability` to model table in druid datasource and its availabillity in the new table availability structure
     * Added class variable for `DataSourceMetadataService` and `ConfigurationLoader` into `AbstractBinderFactory` for application to access

fili-core/src/main/java/com/yahoo/bard/webservice/util/IntervalUtils.java

@@ -4,7 +4,11 @@
 
 import com.yahoo.bard.webservice.config.SystemConfig;
 import com.yahoo.bard.webservice.config.SystemConfigProvider;
+import com.yahoo.bard.webservice.data.time.ZonedTimeGrain;
 import com.yahoo.bard.webservice.druid.model.query.Granularity;
+import com.yahoo.bard.webservice.table.PhysicalTable;
+import com.yahoo.bard.webservice.table.PhysicalTableSchema;
+import com.yahoo.bard.webservice.table.resolver.GranularityComparator;
 
 import org.joda.time.DateTime;
 import org.joda.time.Duration;
@@ -30,6 +34,8 @@
  */
 public class IntervalUtils {
 
+    private static final GranularityComparator COMPARATOR = GranularityComparator.getInstance();
+
     public static final SystemConfig SYSTEM_CONFIG = SystemConfigProvider.getInstance();
 
     public static final String ALIGNMENT_EPOCH_STRING = SYSTEM_CONFIG.getStringProperty(
@@ -209,4 +215,19 @@ public static Optional<DateTime> firstMoment(Collection<? extends Collection<Int
                 .map(Interval::getStart)
                 .reduce(Utils::getMinValue);
     }
+
+    /**
+     * Returns the coarsest ZonedTimeGrain among a set of PhysicalTables.
+     *
+     * @param physicalTables  A set of PhysicalTables among which the coarsest ZonedTimeGrain is to be found.
+     *
+     * @return the coarsest ZonedTimeGrain among a set of PhysicalTables
+     */
+    public static Optional<ZonedTimeGrain> getCoarsestTimeGrain(Collection<PhysicalTable> physicalTables) {
+        return physicalTables.stream()
+                .sorted(COMPARATOR)
+                .findFirst()
+                .map(PhysicalTable::getSchema)
+                .map(PhysicalTableSchema::getTimeGrain);
+    }
 }

fili-core/src/test/groovy/com/yahoo/bard/webservice/util/IntervalUtilsSpec.groovy

@@ -3,12 +3,18 @@
 package com.yahoo.bard.webservice.util
 
 import static com.yahoo.bard.webservice.data.time.DefaultTimeGrain.DAY
+import static com.yahoo.bard.webservice.data.time.DefaultTimeGrain.HOUR
+import static com.yahoo.bard.webservice.data.time.DefaultTimeGrain.MINUTE
 import static com.yahoo.bard.webservice.data.time.DefaultTimeGrain.MONTH
+import static com.yahoo.bard.webservice.data.time.DefaultTimeGrain.QUARTER
 import static com.yahoo.bard.webservice.data.time.DefaultTimeGrain.WEEK
 import static com.yahoo.bard.webservice.data.time.DefaultTimeGrain.YEAR
 
+import com.yahoo.bard.webservice.data.time.ZonedTimeGrain
 import com.yahoo.bard.webservice.druid.model.query.AllGranularity
 import com.yahoo.bard.webservice.druid.model.query.Granularity
+import com.yahoo.bard.webservice.table.PhysicalTable
+import com.yahoo.bard.webservice.table.PhysicalTableSchema
 
 import org.joda.time.DateTime
 import org.joda.time.DateTimeZone
@@ -326,6 +332,51 @@ class IntervalUtilsSpec extends Specification {
         DAY   | ["2012-02-03/2017-04-04"] | ["2012-02-03/2012-05-04", "2017-02-03/2017-04-04"]
     }
 
+    @Unroll
+    def "getCoarsestTimeGrain returns coarsest grain in the case of #description"() {
+        given:
+        PhysicalTableSchema schema1 = Mock(PhysicalTableSchema)
+        PhysicalTableSchema schema2 = Mock(PhysicalTableSchema)
+        PhysicalTableSchema schema3 = Mock(PhysicalTableSchema)
+
+        schema1.getTimeGrain() >> new ZonedTimeGrain(timeGrain1, DateTimeZone.forID(timeZone1))
+        schema2.getTimeGrain() >> new ZonedTimeGrain(timeGrain2, DateTimeZone.forID(timeZone2))
+        schema3.getTimeGrain() >> new ZonedTimeGrain(timeGrain3, DateTimeZone.forID(timeZone3))
+
+        PhysicalTable physicalTable1 = Mock(PhysicalTable)
+        PhysicalTable physicalTable2 = Mock(PhysicalTable)
+        PhysicalTable physicalTable3 = Mock(PhysicalTable)
+
+        physicalTable1.getSchema() >> schema1
+        physicalTable2.getSchema() >> schema2
+        physicalTable3.getSchema() >> schema3
+
+        expect:
+        IntervalUtils.getCoarsestTimeGrain(
+                [
+                        physicalTable1,
+                        physicalTable2,
+                        physicalTable3
+                ]
+        ).get() == new ZonedTimeGrain(expectedTimeGrain, DateTimeZone.forID(expectedTimeZone))
+
+        where:
+        timeGrain1 | timeGrain2 | timeGrain3 | timeZone1         | timeZone2             | timeZone3         | expectedTimeGrain | expectedTimeZone  | description
+        DAY        | DAY        | DAY        | 'America/Chicago' | 'America/Los_Angeles' | 'America/Phoenix' | DAY               | 'America/Chicago' | 'same grain but different time zones'
+        MINUTE     | HOUR       | DAY        | 'America/Phoenix' | 'America/Phoenix'     | 'America/Phoenix' | DAY               | 'America/Phoenix' | 'same time zone but different grans'
+        MINUTE     | HOUR       | DAY        | 'America/Chicago' | 'America/Los_Angeles' | 'America/Phoenix' | DAY               | 'America/Phoenix' | 'different grains, with DAY as the coarsest grain, and different time zones'
+        HOUR       | DAY        | WEEK       | 'America/Chicago' | 'America/Los_Angeles' | 'America/Phoenix' | WEEK              | 'America/Phoenix' | 'different grains, with WEEK as the coarsest grain, and different time zones'
+        DAY        | WEEK       | MONTH      | 'America/Chicago' | 'America/Los_Angeles' | 'America/Phoenix' | MONTH             | 'America/Phoenix' | 'different grains, with MONTH as the coarsest grain, and different time zones'
+        WEEK       | MONTH      | QUARTER    | 'America/Chicago' | 'America/Los_Angeles' | 'America/Phoenix' | QUARTER           | 'America/Phoenix' | 'different grains, with QUARTER as the coarsest grain, and different time zones'
+        MONTH      | QUARTER    | YEAR       | 'America/Chicago' | 'America/Los_Angeles' | 'America/Phoenix' | YEAR              | 'America/Phoenix' | 'different grains, with YEAR as the coarsest grain, and different time zones'
+
+    }
+
+    def "getCoarsestTimeGrain returns empty on empty input physical table collections"() {
+        expect:
+        IntervalUtils.getCoarsestTimeGrain([]) == Optional.empty()
+    }
+
     /**
      * Returns the instant at which this year began.
      *